Development of Novel Antibacterial Ti-Nb-Ga Alloys with Low Stiffness for Medical Implant Applications

Author: Rhianna McHendrie

  • Thesis download: available for open access on 14 May 2025.

McHendrie, Rhianna, 2023 Development of Novel Antibacterial Ti-Nb-Ga Alloys with Low Stiffness for Medical Implant Applications, Flinders University, College of Science and Engineering

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With the rising demand for implantable orthopaedic medical devices and the dominance of device-associated failures including infections, extensive research has been prompted into the development of novel biomaterials that can offer desirable characteristics. This thesis therefore aims to design and develop new titanium-based alloys containing minor gallium additions with the aim of offering beneficial antibacterial properties while having a reduced stiffness level to minimise the effect of stress shielding when in contact with bone. This study focuses on the microstructure, mechanical properties, antimicrobial activity, and cytocompatibility to inform the suitability of the designed alloys as orthopaedic biomaterials. Novel Ti-33Nb-xGa alloys (x = 3, 5 wt%) were produced via casting followed by homogenisation treatment, where all results were compared to the currently employed orthopaedic alloy Ti-6Al-4V. Optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) results depicted a single beta (b) phase microstructure in both alloys, where Ti-33Nb-5Ga was also dominated by dendritic alpha (a) phase grains in a b-phase matrix. EDS analysis indicated that the a-phase dendrites in Ti- 33Nb-5Ga were enriched with titanium, while the b-phase was richer in niobium and gallium elements. Differences in the single b-phase grains were mapped with an inverse pole figure (IPF) and were attributed to variances in crystal structure orientations. Mechanical properties were measured using nanoindentation and microhardness methods, where the Young’s modulus for Ti-33Nb-3Ga and Ti-33Nb-5Ga was found to be 75.4 ± 2.4 and 67.2 ± 1.6 GPa respectively, a significant improvement of 37.4% and 44.2% over Ti-6Al-4V. Importantly, both alloys achieved superior antimicrobial properties against Gram-negative P. aeruginosa and Gram-positive S. aureus bacteria. Antibacterial efficacy was noted at up to 90 ± 5% for the 3 wt% alloy and 95 ± 3% for the 5 wt% alloy. These findings signify an important enhancement of the antimicrobial performance by as much as 130.3% and 187.8% when compared to Ti-6Al-4V. No cytotoxicity was observed in hGF cell lines over 24 hours. Cell morphology and cytoskeleton distribution appeared to depict typical morphology with a prominent nucleus, elongated fibroblastic spindle-shaped morphology, and F-actin filamentous stress fibres in a well-defined structure of parallel bundles along the cellular axis. The developed alloys in this work have shown very promising results and are suggested to be further examined towards the use of orthopaedic implant components.

Keywords: Antibacterial, alloys, gallium, materials, medical implants

Subject: Engineering thesis

Thesis type: Masters
Completed: 2023
School: College of Science and Engineering
Supervisor: Reza Hashemi